Conventional electric motors, both rotary and linear, have very poor torque and force density. For heavy lifting applications, mechanical means such as gears and screws are more typically used. Fluidic devices including pneumatic and hydraulic systems are also used. These mechanical methods generally involve noise, wear, backlash, poor shock tolerance, and high reflected inertia. The fluidic methods tend to increase system complexity due to the addition of a fluid system. Fluid systems are also harder to control than electric systems. Due to seal wear, the fluid methods are unreliable and can contaminate sensitive environments when the working fluid leaks.
A polyphase disc reluctance rotary motor is shown in U.S. Pat. No. 3,992,641 incorporated herein by this reference.
Most prior art linear motors operating on the principle of magnetism, however, include permanent magnets or are classified as inductance machines. U.S. Pat. No. 4,864,169, also incorporated herein by this reference, discloses a linear reluctance motor but it is configured such that the magnetic flux produced extends in the direction of the actuation axis. Such a design, however, results in a fairly low force density.
Thus, there exists a need for a high force density linear reluctance motor.